J.Am. Ceran.So,9同1139-114502007) DOl:10.l11551-2916.2007.01609.x c 2007 The American Ceramic Society urna High-Load Friction Behavior of a Hinge Bearing Based on a Carbon/ Silicon Carbide Composite Yani Zhang, Litong Zhang, Laifei Cheng, and Yongdong Xu National Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, Xian, haanxi 710072. China Two onal carbon fiber-reinforced silicon carbide matrix sliding velocity. These hinge bearings were machined from two- (C/SiC) composites used for hinge bearing were prepared by dimensional carbon/silicon carbide(2D-C/SiC) composites with chemical vapor infiltration. The testing and results of unlubri- gh mechanical properties. Additionally, hinge bearing with Ti cated friction behavior of hinge bearing under high-load trans- alloy axle and steel axle were prepared to compare the friction mitting motion was investigated. The effects of load on friction behavior of different sliding couples behavior between different sliding couple were analyzed. Finally worn surfaces and debris were observed by scanning electron microscopy to study the wear mechanism. A constant friction Il. Experimental Procedure obtained on increasing load up to about 5800 N Excellent wear (1) Preparation of C/Sic Composites Used for Hinge resistance and load-carrying ability was demonstrated by low wear and especially small deformation. The samples with different shape were machined from 2D-C/SiC composites, and the composites were prepared by the chemical vapor infiltration(CVi)method. The sequence of the manufac- . Introducti turing steps is described as follows: Step I: The preform with HE use of load-carrying low-mass hot ceramic matrix com round and rectangular cross-sections was shaped by winding osite(CMC) structures for thermal-protection purposes is and lamination of 2D-carbon cloth with plain weave, respec- the best choice to meet the requirements of a cost-effective, re- tively. The fiber content in the preform was about 40 vol %, and ble, and lightweight thermal protection system (TPs). the samples were made as semi-finish products. As the tubes ed for ring and axle had a wall thickness of about 4-5 mm CMC hot structures are defined as load-carrying structures particular attention was paid achieving unifo that are designed with respect to the criteria of lightweight con- ty of thickness, struction and that are able to sustain the high-operational tem- long with fiber content. Then, the carbon preform was infl peratures and thermal loads without failure. The successful trated with pyrolytic carbon, whose thickness was about 200 utilization of CMC structures to meet extreme re-entry condi which resulted in carbon/carbon(C/C) composites. The tions has been demonstrated in body flaps, leading edge seg C/C samples were pretreated with a graphitization process at 1800C for 2 h. Step 2: The C/Sic composites were prepared by ments,rudders,nose cap, nose skirt, chin panel, etc of X-38 CVI of SiC at 1000 C with the prepared C/C composites. Meth- NASA, Houston, TX) a wide variety of tribological components is required to op- Trichlorosilane (MTS, CH3 SiCl3) was used as a precursor. crate in a space environment for long durations and at a very MTS vapor was carried by bubbling hydrogen. Step 3: The ow torque. Satellites and space vehicles use slide and ball bear C/SiC samples were cut and ground to the final shape, minus the ings. Because of limited power available, they must operate with thickness of the SiC coating (about 60-100 um)for oxidation minimum friction. .0 In addition, many of the tribological de protection. The Sic coating was applied in a subsequent CVD operate both in process with a thickness of about 60-100 um. The contact sur e CMCs such as the carbon fiber-reinforced silicon carbide matrix faces of the axle and ring were finally precision machined to (C/SiC) composites have received considerable attention be neet the tight tolerances and sliding cause of the superior friction performance tubes for rotating axles were prepared with a wall thickness of C/SiC composites for friction materials focus on the friction and 4 mm. an inner diameter of 12 mm, and an outer diameter of used for brake disks in airplanes, etc. Ihe of the axle is 120 20 mm with a machining tolerance ofo to +0.05 mm. The length wear performance testing conditions for these disks are generally given with a higl he length on both sides for sliding speed under a constant normal load or pressure connection with shaft coupling and fixing device. The stationary liding have been investigated rings obtained had a thickness of 5 mm, an internal diameter of experimentally under lubrication. -However, some CMC struc tures especially involve the friction and wear behavior under length of 40 mm for friction contact width. Therefore, a tight high temperature, high load, and low sliding velocity conditions thout lubricants in the re-entry atmosphere ensured within the clearance range of -0.05 to -0.15 mm The Ti alloy with the brand of TC4(Ti-6AHV)and the steel This article will present the unlubricated friction behavior of with the composition of 38 CrMnSi were used for a comparative hinge bearing under transmitting motion with high load and low study during the tests (2) Friction Tests of Hinge Bearing The friction behavior of sliding contact between self-mate C/SiC composites can be achieved by a simulation method The scheme of the method is shown in Fig. 1. This simulation 5015 and ational Young Elitists Foundation. China. under Grant A0TAuthor to whom correspondence should be addressed. e-mail: snow@ mail nwpu. method was originally designed to investigate the friction be- ogical components such as hinge bearings for TPS. The sliding couple consisted of a stationary 1139
High-Load Friction Behavior of a Hinge Bearing Based on a Carbon/ Silicon Carbide Composite Yani Zhang,w Litong Zhang, Laifei Cheng, and Yongdong Xu National Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, Xi’an, Shaanxi 710072, China Two-dimensional carbon fiber-reinforced silicon carbide matrix (C/SiC) composites used for hinge bearing were prepared by chemical vapor infiltration. The testing and results of unlubricated friction behavior of hinge bearing under high-load transmitting motion was investigated. The effects of load on friction behavior between different sliding couple were analyzed. Finally, worn surfaces and debris were observed by scanning electron microscopy to study the wear mechanism. A constant friction coefficient between self-mated C/SiC composites of 0.68 was obtained on increasing load up to about 5800 N. Excellent wear resistance and load-carrying ability was demonstrated by low wear and especially small deformation. I. Introduction THE use of load-carrying low-mass hot ceramic matrix composite (CMC) structures for thermal-protection purposes is the best choice to meet the requirements of a cost-effective, reusable, and lightweight thermal protection system (TPS).1–3 CMC hot structures are defined as load-carrying structures that are designed with respect to the criteria of lightweight construction and that are able to sustain the high-operational temperatures and thermal loads without failure. The successful utilization of CMC structures to meet extreme re-entry conditions has been demonstrated in body flaps, leading edge segments, rudders, nose cap, nose skirt, chin panel, etc. of X-38 (NASA, Houston, TX).3–5 A wide variety of tribological components is required to operate in a space environment for long durations and at a very low torque. Satellites and space vehicles use slide and ball bearings. Because of limited power available, they must operate with minimum friction.5,6 In addition, many of the tribological devices must operate both in air and in the vacuum of space. The CMCs such as the carbon fiber-reinforced silicon carbide matrix (C/SiC) composites have received considerable attention because of the superior friction performance.7,8 Many studies of C/SiC composites for friction materials focus on the friction and wear performance used for brake disks in airplanes, etc.9 The testing conditions for these disks are generally given with a high sliding speed under a constant normal load or pressure.10,11 Wear mechanisms in SiC during sliding have been investigated experimentally under lubrication.12 However, some CMC structures especially involve the friction and wear behavior under high temperature, high load, and low sliding velocity conditions without lubricants in the re-entry atmosphere. This article will present the unlubricated friction behavior of hinge bearing under transmitting motion with high load and low sliding velocity. These hinge bearings were machined from twodimensional carbon/silicon carbide (2D-C/SiC) composites with high mechanical properties. Additionally, hinge bearing with Ti alloy axle and steel axle were prepared to compare the friction behavior of different sliding couples. II. Experimental Procedure (1) Preparation of C/SiC Composites Used for Hinge Bearing The samples with different shape were machined from 2D-C/SiC composites, and the composites were prepared by the chemical vapor infiltration (CVI) method. The sequence of the manufacturing steps is described as follows: Step 1: The preform with round and rectangular cross-sections was shaped by winding and lamination of 2D-carbon cloth with plain weave, respectively. The fiber content in the preform was about 40 vol%, and the samples were made as semi-finish products. As the tubes used for ring and axle had a wall thickness of about 4–5 mm, particular attention was paid achieving uniformity of thickness, along with fiber content. Then, the carbon preform was infiltrated with pyrolytic carbon, whose thickness was about 200 nm, which resulted in carbon/carbon (C/C) composites. The C/C samples were pretreated with a graphitization process at 18001C for 2 h. Step 2: The C/SiC composites were prepared by CVI of SiC at 10001C with the prepared C/C composites. Methyltrichlorosilane (MTS, CH3 SiCl3) was used as a precursor. MTS vapor was carried by bubbling hydrogen. Step 3: The C/SiC samples were cut and ground to the final shape, minus the thickness of the SiC coating (about 60–100 mm) for oxidation protection. The SiC coating was applied in a subsequent CVD process with a thickness of about 60–100 mm. The contact surfaces of the axle and ring were finally precision machined to meet the tight tolerances and sliding requirements. The C/SiC tubes for rotating axles were prepared with a wall thickness of 4 mm, an inner diameter of 12 mm, and an outer diameter of 20 mm with a machining tolerance of 0 to 10.05 mm. The length of the axle is 120 mm, including the length on both sides for connection with shaft coupling and fixing device. The stationary rings obtained had a thickness of 5 mm, an internal diameter of 20 mm with a machining tolerance of 0.10 to 0.05 mm, and a length of 40 mm for friction contact width. Therefore, a tight tolerance between the rotating axle and the stationary ring is ensured within the clearance range of 0.05 to 0.15 mm. The Ti alloy with the brand of TC4 (Ti–6Al–4V) and the steel with the composition of 38 CrMnSi were used for a comparative study during the tests. (2) Friction Tests of Hinge Bearing The friction behavior of sliding contact between self-mated C/SiC composites can be achieved by a simulation method. The scheme of the method is shown in Fig. 1. This simulation method was originally designed to investigate the friction behavior of some typical tribological components such as hinge bearings for TPS. The sliding couple consisted of a stationary M. Hoffman—contributing editor This work was supported by the Natural Science Foundation, China, under Grant No. 90405015 and by the National Young Elitists Foundation, China, under Grant No. 50425208. w Author to whom correspondence should be addressed. e-mail: snow@mail.nwpu. edu.cn Manuscript No. 21843. Received May 29, 2006; approved January 27, 2007. Journal J. Am. Ceram. Soc., 90 [4] 1139–1145 (2007) DOI: 10.1111/j.1551-2916.2007.01609.x r 2007 The American Ceramic Society 1139
1140 Journal of the American Ceramic Society-Zhang et al. Vol. 90. No. 4 C/SiC late CsIc stationary ring際 Shaft coupling ③ C/SiC rotating axle C/SiC side plates orque Bolt Y Testing room C/SiC lower plate Load Fig 1. Schematic of the friction system of hinge bearing based on C/SiC composites. ring and a rotating axle. The load the sliding velocity, and th Y is the radial direction that is vertical to z. and y is the lengt friction torque of samples can be well controlled and measured direction of the axle. to investigate the wear distribution over during tests. As shown in Fig. 1, both the ring and the rotating the length of the ring and axle, the wear was measured in three axle go through the sandwich plates, and the upper plate was for positions marked as a, b, and c in Fig. 1. To obtain the loading load-on purpose. The stationary ring is a tube just as one part effect on the wear rate of the ring and axle. the wear in Z and x and is fixed in the plates. The rotating axle is also a tube, and is erections was measured in the same way. Owing to a rotation by the shaft coupling at one end and connected with a effect, the maximum and the minimum depths of the material fixing device without affecting rotation at the other end. It must emoved from the axle was measured along the circumference be mentioned that equal up-loads and down-loads were applied after the tests instead of in the z and x directions with this during the tests. Although the ring is like a bending load(sec- information the wear distribution of the axle along the circum- tions a and c being pulled down and section b being pulled u ference can be determined. The deformation data of the rotating the axle would be seen as a compressive load along the radial axle and stationary ring are shown in Table Il. The deformation direction due to the hape strength along the overall length s obtained by the difference of diameter after the tests(the dif- of the ring. The loads were operated on the sliding couple ference in the outer diameter of the axle, the difference in the through the C/sic plates. The lower plate was connected by inner diameter of the ring)compared with the original diameter several C/sic bolts with the other two side plates. Both the up- before tests er and the lower plates were located in a load-on instrument Instron 8871, High Wycombe, U. K )to perform the loads on a (3) Measurement of Density and Observation of Surface friction system. Thereby, the data of loads during tests were Microstructure obtained in the data acquisition system by Instron. The data of sliding velocity and friction t can also be measured The microstructure was investigated by scanning electron mi- controlled by a computer. The friction behavior between differ roscopy (SEM, $4700, Hitachi, Tokyo, Japan)analysis. The ent sliding couples can be studied by changing the ring and axle. actual densities of the specimens were measured by the archi- medes method, and the open porosity of the samples was ob- self-mated C/SiC composites, C/Sic composites tested against a tained by the following equations Ti alloy, and C/Sic composites tested against steel, respectively The load applied on the rotating axle can be up to about 6 kN p=mpo(m-mo (1) nd the sliding velocity can be retained with a minimum value of about 33 10 m/s(calculated from the rotation velocity of P=(m1-m)/(m1-m) vestigate the effect of loads property of C/siC composites and to compare with the Ti alloy where p is the real density of the sample df thweighple, m is the and steel, the load was continuously increased with a speed of sample weight in air (g), mo is the sample weight in distilled of 33x10-3m/s. The effect of sliding velocity on friction be- water(g), and m is the sample weight measured after immersing havior was determined at a rotation velocity with an increase in boiling water for 24 h and then wiping(g) step of I7×10m/s(32rpm)from33×10to84×10m/s (80 rpm) and a constant load of IkN (4) Measurement of Mechanical Properties he wear of materials was measured by a micrometer after The mechanical properties of the 2D-C/SiC composites prepared the sliding couple operated for 300s(=5 min)at a constant for hinge b were investigated under tensile, compressive soo g velocity of 33x 10-3m/s and an increasing load up to bending, and shear loading. The samples for measurement were N. The wear rate of um/r was the depth of the material cut from the original C/SiC bulk materials. The sample sizes round. and was the value of the were 106 mm x 3 mm x3.5 mm for the tension test. 20 mm x divided by 5x 32 round. As shown in Fig. I, three direction 10 mm 3 mm for the compressive test, 60 mm x 5 mm x were marked. Z is the loading direction of the ring and axle. 3. 5 mm for the bending test, and 30 mm x 15 mm x 6 mm for
ring and a rotating axle. The load, the sliding velocity, and the friction torque of samples can be well controlled and measured during tests. As shown in Fig. 1, both the ring and the rotating axle go through the sandwich plates, and the upper plate was for load-on purpose. The stationary ring is a tube just as one part, and is fixed in the plates. The rotating axle is also a tube, and is driven by the shaft coupling at one end and connected with a fixing device without affecting rotation at the other end. It must be mentioned that equal up-loads and down-loads were applied during the tests. Although the ring is like a bending load (sections a and c being pulled down and section b being pulled up), the axle would be seen as a compressive load along the radial direction due to the tube-shape strength along the overall length of the ring. The loads were operated on the sliding couple through the C/SiC plates. The lower plate was connected by several C/SiC bolts with the other two side plates. Both the upper and the lower plates were located in a load-on instrument (Instron 8871, High Wycombe, U.K.) to perform the loads on a friction system. Thereby, the data of loads during tests were obtained in the data acquisition system by Instron. The data of sliding velocity and friction torque can also be measured and controlled by a computer. The friction behavior between different sliding couples can be studied by changing the ring and axle. In the present work, three different sliding couples were studied: self-mated C/SiC composites, C/SiC composites tested against a Ti alloy, and C/SiC composites tested against steel, respectively. The load applied on the rotating axle can be up to about 6 kN and the sliding velocity can be retained with a minimum value of about 33 103 m/s (calculated from the rotation velocity of 32 rpm). To investigate the effect of loads on the friction property of C/SiC composites and to compare with the Ti alloy and steel, the load was continuously increased with a speed of 10 N/s and the sliding velocity was controlled at a constant value of 33 103 m/s. The effect of sliding velocity on friction behavior was determined at a rotation velocity with an increase step of 17 103 m/s (32 rpm) from 33 103 to 84 103 m/s (80 rpm) and a constant load of 1 kN. The wear of materials was measured by a micrometer after the sliding couple operated for 300 s ( 5 5 min) at a constant sliding velocity of 33 103 m/s and an increasing load up to 3500 N. The wear rate of mm/r was the depth of the material removed per round, and was the value of the removed depth divided by 5 32 round. As shown in Fig. 1, three directions were marked. Z is the loading direction of the ring and axle, X is the radial direction that is vertical to Z, and Y is the length direction of the axle. To investigate the wear distribution over the length of the ring and axle, the wear was measured in three positions marked as a, b, and c in Fig. 1. To obtain the loading effect on the wear rate of the ring and axle, the wear in Z and X directions was measured in the same way. Owing to a rotation effect, the maximum and the minimum depths of the material removed from the axle was measured along the circumference after the tests instead of in the Z and X directions. With this information, the wear distribution of the axle along the circumference can be determined. The deformation data of the rotating axle and stationary ring are shown in Table II. The deformation is obtained by the difference of diameter after the tests (the difference in the outer diameter of the axle, the difference in the inner diameter of the ring) compared with the original diameter before tests. (3) Measurement of Density and Observation of Surface Microstructure The microstructure was investigated by scanning electron microscopy (SEM, S-4700, Hitachi, Tokyo, Japan) analysis. The actual densities of the specimens were measured by the Archimedes method, and the open porosity of the samples was obtained by the following equations r ¼ mr0ðm m0Þ (1) P ¼ ðm1 mÞ=ðm1 m0Þ (2) where r is the real density of the sample (g/cm3 ), r0 is the density of water (g/cm3 ), P is the open porosity of the sample, m is the sample weight in air (g), m0 is the sample weight in distilled water (g), and m1 is the sample weight measured after immersing in boiling water for 24 h and then wiping (g). (4) Measurement of Mechanical Properties The mechanical properties of the 2D-C/SiC composites prepared for hinge bearing were investigated under tensile, compressive, bending, and shear loading. The samples for measurement were cut from the original C/SiC bulk materials. The sample sizes were 106 mm 3 mm 3.5 mm for the tension test, 20 mm 10 mm 3 mm for the compressive test, 60 mm 5 mm 3.5 mm for the bending test, and 30 mm 15 mm 6 mm for Fig. 1. Schematic of the friction system of hinge bearing based on C/SiC composites. 1140 Journal of the American Ceramic Society—Zhang et al. Vol. 90, No. 4
April 2007 High-Load Friction of a C/SiC Hinge Bearing 114l 3M 2 Fig. 2. Microstructure of prepared two-dimensional carbon/silicon carbide composites. (a) The cross-section of the prepared sample; (b) the amplified cross-section of the prepared sample. I-longitudinal fibers, 2-transverse fibers. 3--matrix around fiber clusters, 4---matrix around a single fiber. Table 1. Mechanical Properties of the 2D-C/SiC Composites an alteration of the interfacial bonding between the fiber and matrix. The tensile stress within the interfacial phase along the fiber radial direction was generated after the composites cooled Items Unit Results at room temperature down from the infiltration temperature to room temperature Density 2.03 Thereby, it was easy for the carbon fiber to debond and be Open porosity pulled out from the C/Sic(Fig. 3(b). Under tensile and flexural Tensile strength MP 245 load, the cracks first developed and expanded in SiC coating Flexural strength MPa The single fiber and fiber cluster pullout from the matrix indi Compression strength MPa cated a non-brittle failure behavior of the composites. No fibers Inter-laminar shear strength MPa were introduced to the direction vertical into carbon cloth lam- ination in the structure of 2D-C/SiC composites, which resulted 2D-C/SiC, two-dimensional carbon/silicon carbic in high tensile, flexural, and compressive strength but low shear strength. The tensile strength and flexural strength of the C/sic composites were 245 MPa and 450 MP, respectively. The com- le inter-laminar shear test. All the measurements of mechanica pression strength was 360 MPa. The mismatch along the fiber rties were performed on an Instron 8871 test machine, at a axis of thermal expansion coefficients(TECs)between the C/SiC locity of 0.005 mr and the fiber resulted in many micro-cracks in the matrix. These micro-cracks made some contribution to the non-brittle failure IIL Results and discussion behavior by deflection of the main cracks. It is concluded that the 2D-C/sic composites exhibit excellent tensile, flexural, and (1) Mechanical Properties compression strength but low shear strength, as it could be The density and porosity of the 2D-C/SiC composites used for expected. nge bearing were 2.03 g/cm and 12%, respectively. Figure 2 shows the microstructure of the prepared C/Sic composi The transverse fibers and the longitudinal fibers as marked in (2) Effect of loads on Friction Behavior Fig. 2(a)show the woven characteristic structure of 2D-C/Sic Friction is the resistance to movement when one object moves composites. The matrix around the fiber clusters and the matrix relative to another while in contact. there is a basic law of fric- around the single fiber can be found in Figs. 2(a) and (b). The tion: the friction force f is proportional to the normal force F, mechanical properties of the composites were investigated under which leads to the relationship: f= uf, where u is defined as the tensile, compressive, bending, and shear loading. The corre- coefficient of friction. In this paper, the friction behavior be- sponding strength data are listed in Table l, and the microstruc- tween self-mated C/SiC composites was investigated. The sliding tural observation of different failure behavior is shown in Fig. 3 couple was a self-mated C/Sic stationary ring and a rotating The variation of failure behavior of composites was caused by ig. 3. Scanning electron micrograph of a carbon fiber reinforced silicon carbide matrix-damaged specimen under different loads. (a)under a tensile d, (b) under a flexural load
the inter-laminar shear test. All the measurements of mechanical properties were performed on an Instron 8871 test machine, at a loading velocity of 0.005 mm/min. III. Results and Discussion (1) Mechanical Properties The density and porosity of the 2D-C/SiC composites used for hinge bearing were 2.03 g/cm3 and 12%, respectively. Figure 2 shows the microstructure of the prepared C/SiC composites. The transverse fibers and the longitudinal fibers as marked in Fig. 2(a) show the woven characteristic structure of 2D-C/SiC composites. The matrix around the fiber clusters and the matrix around the single fiber can be found in Figs. 2(a) and (b). The mechanical properties of the composites were investigated under tensile, compressive, bending, and shear loading. The corresponding strength data are listed in Table I, and the microstructural observation of different failure behavior is shown in Fig. 3. The variation of failure behavior of composites was caused by an alteration of the interfacial bonding between the fiber and matrix. The tensile stress within the interfacial phase along the fiber radial direction was generated after the composites cooled down from the infiltration temperature to room temperature. Thereby, it was easy for the carbon fiber to debond and be pulled out from the C/SiC (Fig. 3(b)). Under tensile and flexural load, the cracks first developed and expanded in SiC coating. The single fiber and fiber cluster pullout from the matrix indicated a non-brittle failure behavior of the composites. No fibers were introduced to the direction vertical into carbon cloth lamination in the structure of 2D-C/SiC composites, which resulted in high tensile, flexural, and compressive strength but low shear strength. The tensile strength and flexural strength of the C/SiC composites were 245 MPa and 450 MP, respectively. The compression strength was 360 MPa. The mismatch along the fiber axis of thermal expansion coefficients (TECs) between the C/SiC and the fiber resulted in many micro-cracks in the matrix. These micro-cracks made some contribution to the non-brittle failure behavior by deflection of the main cracks. It is concluded that the 2D-C/SiC composites exhibit excellent tensile, flexural, and compression strength but low shear strength, as it could be expected. (2) Effect of Loads on Friction Behavior Friction is the resistance to movement when one object moves relative to another while in contact. There is a basic law of friction: the friction force f is proportional to the normal force F, which leads to the relationship: f 5 mF, where m is defined as the coefficient of friction. In this paper, the friction behavior between self-mated C/SiC composites was investigated. The sliding couple was a self-mated C/SiC stationary ring and a rotating axle. Fig. 2. Microstructure of prepared two-dimensional carbon/silicon carbide composites. (a) The cross-section of the prepared sample; (b) the amplified cross-section of the prepared sample. 1—longitudinal fibers, 2—transverse fibers, 3—matrix around fiber clusters, 4—matrix around a single fiber. Table I. Mechanical Properties of the 2D-C/SiC Composites Used for Hinge Bearing Items Unit Results at room temperature Density g/cm3 2.03 Open porosity % 12 Tensile strength MPa 245 Flexural strength MPa 450 Compression strength MPa 360 Inter-laminar shear strength MPa 28 2D-C/SiC, two-dimensional carbon/silicon carbide. Fig. 3. Scanning electron micrograph of a carbon fiber reinforced silicon carbide matrix-damaged specimen under different loads. (a) under a tensile load, (b) under a flexural load. April 2007 High-Load Friction of a C/SiC Hinge Bearing 1141
1142 Journal of the American Ceramic Society--Zhang et al. Vol. 90. No. 4 4500 4000 x test 1 ▲test2 A 0000 ◆test3 28y 5030505 css 10 0000000 1000 100200300400500 Time(s) 0100020003000400050006000 1- Sliding velocity, 2- Load; 3- Friction force Fig. 6. Effect of sliding velocity on the friction force of self-mated car- ig. 4. Relationship of friction force and load of self-mated carbon bon fiber reinforced silicon carbide matrix composites under a constant fiber reinforced silicon carbide matrix composites under a constant slid- load of 1 kN The effect of loads on the friction behavior of C/Sic com- relationship between friction force and load for C/SiC composite posites was studied by increasing loads under a constant sliding was again found, as shown in Fig. 5. However, a non-linear re- velocity Figure 4 shows the relationship of friction force and the lation between friction force and load was obtained in the two new normal loads. The friction force increased with increasing loads sliding couples of the Ti alloy and steel axle and a linear relationship was similarly found between friction It was concluded that the friction coefficient is constant and force and loads when three tests were conducted. The C/SiC dependent of the applied load between self-mated C/SiC com- composites rotating axle was still in a good working condition osites, but it is not constant when C/SiC composites friction hen the friction force was 4 kN with a normal load of 5800 N. against a Ti alloy or steel. No debris was found from the friction system during the tests The friction force is proportional to the load, which indicates friction coefficient between self-mated C/SiC ( 4) Efect of Sliding Velocity on Friction Be constant within the frame of the test parameters. The Two basic laws of friction are that the friction force is inde- Defficient of the line in Fig 4 that represented the friction pendent of the apparent area of contact and the friction force is oefficient was about 0.68 ndependent of the sliding velocity. There are some exceptions to these laws, especially in vacuum, but for most situations they are (3) Comparison Studies on Friction Behavior of C/sic applicable Composites, Ti Alloy, and Steel The friction behavior between self-mated C/SiC composites A comparison of friction behavior between three kinds of sliding under different sliding velocities was investigated. Under a con- couples at a constant sliding velocity was made. The stationa stant load, the friction force was tested by changing the sliding ring was a C/Sic composite, and the rotating axle was tested wi velocity. As shown in Fig. 6, the friction force almost retaine C/SiC composites, Ti alloy, and steel, respectively the same changing trend with the load when the load increased ents the relationship of friction force and loads for the three kinds to a constant level of i kn. the friction force remained constant of materials. The friction force for all the three kinds of materials at 750 N with elevated sliding velocity. This result indicated that increased with elevated loads The friction force of the two new the coefficient of friction is constant and is independent of sliding couples increased much faster that that of self-mated C/SiC sliding velocity within the frame of the chosen parameters in composites. When the load was up to 3 kN, the friction forces of the test It icluded that the coefficient of friction between self- the C/SiC composites, Ti alloy, and steel were 2400, 3300, and mated C/SiC composites is independent of sliding velocity, 3900 N, respectively. The friction noise and the falling of mass debris were found between the two new sliding couples. A linear which suggested a stable friction property of C/SiC composites (5) Effects of Loads on Wear and Material Deformation There are basically two reasons why friction occurs. The first is ◆c/ Sic composites due to adhesion that occurs between the molecules of the two ▲Taoy are not absolutely flat. When a hard surface slides across a softer surface, small asperities on the hard surface"plow'through the soft surface. This is known as abrasion. However. between the self-mated C/SiC composites as shown in Fig. 1, the friction is mainly dependent on the contact state, the tightness as well as the deformation between contact surfaces. In this paper, th friction system is operated under high loads up to 5-6 kN, which equired good load-carrying abi 500 y of both the stationary ring and the rotating axle to avoid plastic deformation The deformation along the diameter of both the ring and axle 0 500 1000 1500 2000 2500 3000 3500 4000 was measured after the tests as listed in Table Il. It was found that the deformation between self-mated C/SiC composites was Load (N) obviously smaller than that between the C/Sic composite's ring Fig. 5. Friction force versus the loads of carbon fiber reinforced and the Ti alloy axle. The deformation of C/Sic ring caused by arbide matrix(C/SiC)composites, Ti alloy, and steel friction the Ti alloy axle was 10 times higher than that by the C/sic C/SiC composites under a constant shding velocity of 33 x 10 omposite itself
The effect of loads on the friction behavior of C/SiC composites was studied by increasing loads under a constant sliding velocity. Figure 4 shows the relationship of friction force and the normal loads. The friction force increased with increasing loads, and a linear relationship was similarly found between friction force and loads when three tests were conducted. The C/SiC composites’ rotating axle was still in a good working condition when the friction force was 4 kN with a normal load of 5800 N. No debris was found from the friction system during the tests. The friction force is proportional to the load, which indicates that the friction coefficient between self-mated C/SiC composites was constant within the frame of the test parameters. The slope coefficient of the line in Fig. 4 that represented the friction coefficient was about 0.68. (3) Comparison Studies on Friction Behavior of C/SiC Composites, Ti Alloy, and Steel A comparison of friction behavior between three kinds of sliding couples at a constant sliding velocity was made. The stationary ring was a C/SiC composite, and the rotating axle was tested with C/SiC composites, Ti alloy, and steel, respectively. Figure 5 presents the relationship of friction force and loads for the three kinds of materials. The friction force for all the three kinds of materials increased with elevated loads. The friction force of the two new sliding couples increased much faster that that of self-mated C/SiC composites. When the load was up to 3 kN, the friction forces of the C/SiC composites, Ti alloy, and steel were 2400, 3300, and 3900 N, respectively. The friction noise and the falling of mass debris were found between the two new sliding couples. A linear relationship between friction force and load for C/SiC composites was again found, as shown in Fig. 5. However, a non-linear relation between friction force and load was obtained in the two new sliding couples of the Ti alloy and steel axle. It was concluded that the friction coefficient is constant and independent of the applied load between self-mated C/SiC composites, but it is not constant when C/SiC composites friction against a Ti alloy or steel. (4) Effect of Sliding Velocity on Friction Behavior Two basic laws of friction are that the friction force is independent of the apparent area of contact and the friction force is independent of the sliding velocity. There are some exceptions to these laws, especially in vacuum, but for most situations they are applicable. The friction behavior between self-mated C/SiC composites under different sliding velocities was investigated. Under a constant load, the friction force was tested by changing the sliding velocity. As shown in Fig. 6, the friction force almost retained the same changing trend with the load. When the load increased to a constant level of 1 kN, the friction force remained constant at 750 N with elevated sliding velocity. This result indicated that the coefficient of friction is constant and is independent of sliding velocity within the frame of the chosen parameters in the test. It is concluded that the coefficient of friction between selfmated C/SiC composites is independent of sliding velocity, which suggested a stable friction property of C/SiC composites. (5) Effects of Loads on Wear and Material Deformation There are basically two reasons why friction occurs. The first is due to adhesion that occurs between the molecules of the two contact surfaces. The second is due to the fact that the surfaces are not absolutely flat. When a hard surface slides across a softer surface, small asperities on the hard surface ‘‘plow’’ through the soft surface. This is known as abrasion. However, between the self-mated C/SiC composites as shown in Fig. 1, the friction is mainly dependent on the contact state, the tightness as well as the deformation between contact surfaces. In this paper, the friction system is operated under high loads up to 5–6 kN, which required good load-carrying ability of both the stationary ring and the rotating axle to avoid plastic deformation. The deformation along the diameter of both the ring and axle was measured after the tests as listed in Table II. It was found that the deformation between self-mated C/SiC composites was obviously smaller than that between the C/SiC composite’s ring and the Ti alloy axle. The deformation of C/SiC ring caused by the Ti alloy axle was 10 times higher than that by the C/SiC composite itself. Fig. 5. Friction force versus the loads of carbon fiber reinforced silicon carbide matrix (C/SiC) composites, Ti alloy, and steel friction against C/SiC composites under a constant sliding velocity of 33 103 m/s. Fig. 6. Effect of sliding velocity on the friction force of self-mated carbon fiber reinforced silicon carbide matrix composites under a constant load of 1 kN. Fig. 4. Relationship of friction force and load of self-mated carbon fiber reinforced silicon carbide matrix composites under a constant sliding velocity of 33 103 m/s. 1142 Journal of the American Ceramic Society—Zhang et al. Vol. 90, No. 4
April 2007 High-Load Friction of a C/SiC Hinge Bearing 1143 Table Il. Deformation of Rotating Axle and Stationary ring in Different Sliding Couples After Tests a c/SiC axle. Max Deformation in different test positions (mm) ▲ C/SiC axle,M Sliding couple Testing objects 0.01 0.02 0.01 c04 △ n alloy axe,Max C/SiC axle 0.008 0.010 0012 o Ti alloy axe, Min C/SiC ring 0.10 0.20 0.16 Ti alloy axle 0.020 0.016 0.020 合▲b C/SiC, carbon/silicon carbide. Testing position The wear rate of um/r was the depth of the material removed te of a carbon fiber reinforced silicon carbide matrix composite rings tested against c/Sic composites and a ti alloy, (cdic) i m a Ti alloy axle tested against a CSiC stationary ring respectively. A lower wear rate and lower difference in wear rate -5kN and a constant sliding velocity of 33 x 10 m/s. in Z and X directions of the C/SiC ring were found when tested against C/SiC composites than that against Ti alloy. The wear Figure 9 shows the micrograph and EDS spectra of wear de- bris in the sliding couple of self-mated C/SiC composites after times higher than that of self-mated C/SiC composites. Thereb tests under an increasing load up to 3500 N and a constant slid- the wear rate and the resulting deformation of the C/sic com- ing velocity of 33 x 10 m/s. The contact surfaces were covered osite ring caused by the C/Sic composites were much lower with wear debris and wear grain as shown in Fig 9(a). The wear than that caused by the ti alloy. debris that remained in the wear track was ground to a very fine The high-wear rate caused by the Ti alloy and the loading powder by continuous rubbing. The EDS spectra of wear debris effect on the z direction resulted in an elliptical cross section of dicated no chemical change in the composition of Sic debris the ring. However, the axle was worn in the whole circumference This is mainly related to the low sliding velocity, which makes direction due to the rotation effect although the loading effect apid temperature increase of the contact surface difficult. The was still on the axle; hence the cross-section shape of axle did formation of wear debris and tribochemical layer for the si not c based composites does not always occur under different sliding Figure 8 presents the wear rate of the axles after tests conditions. The formation of wear debris is very sensitive to the C/sic composite ring. An obviously lower wear rate e environment(humidity), and it occurs mostly by fracture on C/SiC composite axle was found. The differences in th different scales: microfracture at low loads, grain boundary fa imum and maximum wear rate of both the C/Sic compos tigue at intermediate loads, and macroscopic fracture at high Ti alloy axle along the circumference were small because the axle ads. In a dry ambient, this powder has a low mechanical tained a rotation state and was worn along the sliding direc- strength and has very little influence on wear. In a humid am tion per round during the tests bient, the phenomena depend on the material. In water and It was concluded that the Csic composites demonstrated some aqueous solutions, Sic dissolves in water and does not good wear resistance and load-carrying ability due to its low ate and the resulting small deformation under high loads dominated by fracture proc biochemical reaction pi With a friction duration of 5 min, the wear rate of the C/sic ucts may be present to moderate the stress distribution by pro- per round, which was only 1/10-1/ viding a reaction layer for wear protection. Thereby, perhaps 20 that of the Ti alloy. The deformation of the C/siC comp there exists a potential for the existence of a tribochemical laye caused by the C/sic composites was <0.02 mm after the tests under high speed conditions or in wet environments, such as under high loads, which was only 1/10 of that caused by the ti brake disks under braking tests, in which the than 40 m/s. However, under a low sliding speed of about 0.03 s, no chemical change but a smooth tribo-layer is found on (6) Microstructure on Contact Surfaces the contact surface. As another example, a hydrated silicic oxide film forms during sliding in the Sic/Sic couple. However, The wear-induced surfaces are significantly determined by the the time required to form this film increases with increasing ap- abrasion and damage mechanism on the contact surfaces of the plied load. When the wear debris are removed continuously sliding couple. The smooth annuluses with a metal-like luster were observed on the contact surfaces of the C/Sic composite during sliding. the oxide film does not form The wear was significantly determined by high load and cyclic ing axle were investigated by the of the C/SiC composite rotat- mechanical stresses. The obvious shallow grooves along with the sliding direction were obtained on the contact surface after fric- tion tests. This is the result of the relative movements of contact conjunctions or asperities. The microstructure of contact sur a Z with Ti alloy axe faces at different testing positions a, b, and c on the C/sic axl before and after tests was observed. as Fig. 10 shows. As show △X, with Ti alloy axe in Fig. 10(a), the as-machined contact surface is rough and the material is discontinuous in microscopy before the tests, althoug xz- with C/Sic ade it is plat by macroscopic observation. However, a smooth tri- bo-layer with more compact materials and metal-like luster 0.5 X- with C/sic axle Figs. 11(bd))is observed after the tests. The wear degrees at testing positions a, b, and c are different. The nearer the positie approaches the shaft coupling(marked as c in Fig. 1), the smoother the surface (as shown in Fig. 10(d). As the rotatio Testing position of the axle in the sliding couple of hinge bearing is a transmission mode from the driving side by shaft coupling to the other side. Fig. 7. Wear rate of a carbon fiber reinforced silicon carbide matrix position c will be the earliest contact point per round The contact surfaces of the C/Sic axle after tests under dif- under a load of 3.5 kN and a constant sliding velocity of 33 x 10-3m/s. ferent loads were investigated by SEM. No large microstructural
The wear rate of mm/r was the depth of the material removed per round. Figure 7 shows the radial wear rate of the C/SiC composite rings tested against C/SiC composites and a Ti alloy, respectively. A lower wear rate and lower difference in wear rate in Z and X directions of the C/SiC ring were found when tested against C/SiC composites than that against Ti alloy. The wear rate of C/SiC composites caused by the Ti alloy was about 10–20 times higher than that of self-mated C/SiC composites. Thereby, the wear rate and the resulting deformation of the C/SiC composite ring caused by the C/SiC composites were much lower than that caused by the Ti alloy. The high-wear rate caused by the Ti alloy and the loading effect on the Z direction resulted in an elliptical cross section of the ring. However, the axle was worn in the whole circumference direction due to the rotation effect although the loading effect was still on the axle; hence, the cross-section shape of axle did not change obviously. Figure 8 presents the wear rate of the axles after tests against the C/SiC composite ring. An obviously lower wear rate of the C/SiC composite axle was found. The differences in the minimum and maximum wear rate of both the C/SiC composite and Ti alloy axle along the circumference were small because the axle retained a rotation state and was worn along the sliding direction per round during the tests. It was concluded that the C/SiC composites demonstrated good wear resistance and load-carrying ability due to its low wear rate and the resulting small deformation under high loads. With a friction duration of 5 min, the wear rate of the C/SiC composites was about 0.1 mm per round, which was only 1/10–1/ 20 that of the Ti alloy. The deformation of the C/SiC composites caused by the C/SiC composites was o0.02 mm after the tests under high loads, which was only 1/10 of that caused by the Ti alloy. (6) Microstructure on Contact Surfaces The wear-induced surfaces are significantly determined by the abrasion and damage mechanism on the contact surfaces of the sliding couple. The smooth annuluses with a metal-like luster were observed on the contact surfaces of the C/SiC composite axle. The surface microstructures of the C/SiC composite rotating axle were investigated by the SEM analysis. Figure 9 shows the micrograph and EDS spectra of wear debris in the sliding couple of self-mated C/SiC composites after tests under an increasing load up to 3500 N and a constant sliding velocity of 33 103 m/s. The contact surfaces were covered with wear debris and wear grain as shown in Fig. 9(a). The wear debris that remained in the wear track was ground to a very fine powder by continuous rubbing. The EDS spectra of wear debris indicated no chemical change in the composition of SiC debris. This is mainly related to the low sliding velocity, which makes rapid temperature increase of the contact surface difficult. The formation of wear debris and tribochemical layer for the SiCbased composites does not always occur under different sliding conditions. The formation of wear debris is very sensitive to the environment (humidity), and it occurs mostly by fracture on different scales: microfracture at low loads, grain boundary fatigue at intermediate loads, and macroscopic fracture at high loads. In a dry ambient, this powder has a low mechanical strength and has very little influence on wear. In a humid ambient, the phenomena depend on the material. In water and some aqueous solutions, SiC dissolves in water and does not form wear debris.13 Although ceramic wear mechanisms are dominated by fracture processes, tribochemical reaction products may be present to moderate the stress distribution by providing a reaction layer for wear protection.14 Thereby, perhaps there exists a potential for the existence of a tribochemical layer under high speed conditions or in wet environments, such as brake disks under braking tests, in which the speed is higher than 40 m/s. However, under a low sliding speed of about 0.03 m/s, no chemical change but a smooth tribo-layer is found on the contact surface. As another example, a hydrated silicium oxide film forms during sliding in the SiC/SiC couple. However, the time required to form this film increases with increasing applied load. When the wear debris are removed continuously during sliding, the oxide film does not form.15 The wear was significantly determined by high load and cyclic mechanical stresses. The obvious shallow grooves along with the sliding direction were obtained on the contact surface after friction tests. This is the result of the relative movements of contact conjunctions or asperities. The microstructure of contact surfaces at different testing positions a, b, and c on the C/SiC axle before and after tests was observed, as Fig. 10 shows. As shown in Fig. 10(a), the as-machined contact surface is rough and the material is discontinuous in microscopy before the tests, although it is plat by macroscopic observation. However, a smooth tribo-layer with more compact materials and metal-like luster (Figs. 11(b)–(d)) is observed after the tests. The wear degrees at testing positions a, b, and c are different. The nearer the position approaches the shaft coupling (marked as c in Fig. 1), the smoother the surface (as shown in Fig. 10(d)). As the rotation of the axle in the sliding couple of hinge bearing is a transmission mode from the driving side by shaft coupling to the other side, position c will be the earliest contact point per round. The contact surfaces of the C/SiC axle after tests under different loads were investigated by SEM. No large microstructural Fig. 7. Wear rate of a carbon fiber reinforced silicon carbide matrix (C/SiC) stationary ring tested against a C/SiC axle and a Ti alloy axle under a load of 3.5 kN and a constant sliding velocity of 33 103 m/s. Table II. Deformation of Rotating Axle and Stationary Ring in Different Sliding Couples After Tests Sliding couple Testing objects Deformation in different test positions (mm) abc 1 C/SiC ring 0.01 0.02 0.01 C/SiC axle 0.008 0.010 0.012 2 C/SiC ring 0.10 0.20 0.16 Ti alloy axle 0.020 0.016 0.020 C/SiC, carbon/silicon carbide. Fig. 8. Wear rate of a carbon fiber reinforced silicon carbide matrix (C/SiC) axle and a Ti alloy axle tested against a C/SiC stationary ring under a load of 3.5 kN and a constant sliding velocity of 33 103 m/s. April 2007 High-Load Friction of a C/SiC Hinge Bearing 1143
1144 Journal of the American Ceramic Society--Zhang et al. Vol. 90. No. 4 5432 0 67 200ur Energy /kev Scanning electron micrograph and EDS spectra of wear debris of self-mated C/SiC composites tested under a load of 3.5 kN and a constant g velocity change was obtained after tested at 1. 3.5. and 5 kN. The main Wear mechanisms of ceramics are predominantly dependent difference was that the surface became more compact and on the tribological contact stresses. At low contact stress, the mother with increasing load. The degree of damage of the removal of material is controlled by plastic deformation-induced urface caused by the groove is mainly dependent on the sliding microfracture on the asperity contact scale. Wear debris are peed and applied load(contact pressure)on the friction surface. produced when the plastic deformation exceeds the plasticity No obvious adhesion phenomena and no peeling occurred on limit of the material. Based on the analysis, the wear between the contact surfaces. No cracks were found on the rotating axle self-mated C/Sic composites did not shift to the severe adhesion after tests under a load of I kN. However, several shallow cracks stage, and still remained in the grain abrasion stage with a mild were observed after tests at a load above 3.5 kn as shown in vear under a high load and a low sliding velocity. The wear Fig. Il. The local high temperature between the contact surfaces debris that remained in the wear track was ground to a very fine during the friction generally plays an important role in the de- powder by continuous rubbing. The smooth and compact tribo- formation of cracks on the surface, especially on the surface that layer formed on the contact surface exhibited several shallow is a coating on the substrate. Sometimes the mismatch of TEcs cracks under a load above 3. 5 kN. the grain abrasion wear is between the coating and the substrate is the main reason for the main wear mechanism of the self-mated C/SiC composite formation of cracks hinge bearing within the framework of the testing conditions 50 um 50 um 50 um Fig 10. Con sliding veloci
change was obtained after tested at 1, 3.5, and 5 kN. The main difference was that the surface became more compact and smoother with increasing load. The degree of damage of the surface caused by the groove is mainly dependent on the sliding speed and applied load (contact pressure) on the friction surface. No obvious adhesion phenomena and no peeling occurred on the contact surfaces. No cracks were found on the rotating axle after tests under a load of 1 kN. However, several shallow cracks were observed after tests at a load above 3.5 kN as shown in Fig. 11. The local high temperature between the contact surfaces during the friction generally plays an important role in the deformation of cracks on the surface, especially on the surface that is a coating on the substrate. Sometimes, the mismatch of TECs between the coating and the substrate is the main reason for formation of cracks. Wear mechanisms of ceramics are predominantly dependent on the tribological contact stresses. At low contact stress, the removal of material is controlled by plastic deformation-induced microfracture on the asperity contact scale. Wear debris are produced when the plastic deformation exceeds the plasticity limit of the material.14 Based on the analysis, the wear between self-mated C/SiC composites did not shift to the severe adhesion stage, and still remained in the grain abrasion stage with a mild wear under a high load and a low sliding velocity. The wear debris that remained in the wear track was ground to a very fine powder by continuous rubbing. The smooth and compact tribolayer formed on the contact surface exhibited several shallow cracks under a load above 3.5 kN. The grain abrasion wear is the main wear mechanism of the self-mated C/SiC composite hinge bearing within the framework of the testing conditions. Fig. 10. Contact surfaces of a carbon fiber reinforced silicon carbide matrix (C/SiC) axle before and after friction against a C/SiC ring under constant sliding velocity of 33 103 m/s and a load of 1 kN. (a) As-machined surface on the axle before the tests; (b), (c), and (d) contact surfaces of testing positions a, b, and c on the axle after the tests. Fig. 9. Scanning electron micrograph and EDS spectra of wear debris of self-mated C/SiC composites tested under a load of 3.5 kN and a constant sliding velocity of 33 103 m/s. 1144 Journal of the American Ceramic Society—Zhang et al. Vol. 90, No. 4
April 2007 High-Load Friction of a C/SiC Hinge Bearing 1145 (4) The grain abrasion is the main wear mechanism of a self- mated C/SiC composite hinge bearing with the testing frame- work. The wear was significantly determined by high load and cyclic mechanical stresses. A smooth and compact tribo-layer was formed. and the wear debris that remained in the wear track 3.5 kN led to several shallow cracks on the contact surfac 9to was ground to a very fine powder. The shallow grooves alor the sliding direction were mainly caused by the relative move- ment of contact asperities. Load increased to a level above References H G. Wulz and U. Trabandt, "Large Integral Hot CMC Structures De rs". AIAA-97-2485. Amencan Institute of "R. Kladtke, N. Puttmann, and E. D. Graf, ""X-38 European Partnership AlAA 1999-99-4936, The American Institute of Aeronautics and Astronautics, 10 um Development of Hot CMC Structures for Space Re- xperiments": International Air and Space Symposium Fig. 11. Contact surfaces of carbon fiber reinforced silicon carbide atrix(CSiC) after friction against a CSiC ring under a load of +A Muhlratzer and H. Pfeiffer, "CMC Body Flaps for The X-38 Experimental 3.5 kN and a constant sliding velocity of 33 x 10- m/s Space Vehicle. " Ceran. Eng. Sci. Pro, ABI/INFORM Trade Industry, 23 [31 331-8(2002) rtel, H. Weihs, I. Fischer, and M. Dogigli, "Thermal-Mechanical Q fication Tests of Complex CMC Re-Entry Structures, "Ceram. Eng. Sci. Pro. IV. Conclusions ABI/INFORM Trade Industry, 24 (4)281-1(2003). oue to Tribological Prob- g with required good mechanical prop- NO1 Annual Meeting, Society of Tribologists and Lubrication Engineers, made of 2D-C/Sic composites by CVI. The damaged showed non-brittle failure behavior resulting from the Renz, C/C-SiC Composites for Ad- of a single fiber and fiber cluster. The flexural strength vanced Friction Systems, Adv. Eng. Mater. 4. 427-36(2002). Z S. Pak,"Ct SiC/C Composites for Tribological Application, Key Eng compressive strength were 450 MP and 360 MPa, respectively. Purdy. T. Walker, and S Horst. C/SiC Material Evalu- ( 2) The CVI process offered a potential method to manu- ation or aircraft brake Application. " Key Eug. ater 164-165 802(1999 facture the C/SiC composite hinge bearing of a stable and reli- arbon Silicon Carbide Composite, " Cam. Sci. Tech, 61 [3]417-23 able friction property under a high load. With a material density f 2.03 g/cm, a constant friction coefficient was obtained as 0.68 on increasing the load up to 5800 N. 1153-60002) ( The hinge bearing based on C/SiC composites demon C -D. Um and S.-S. Kim. ""Wear and Wear Transition rated good wear resistance and load-carrying ability due to the T.E. Fischer. Z. Zhu. H. Kim, and D. S. Shin, "Genesis and Role of Wear w wear and the small deformation under high loads. T e wear Vear of Ceramics, Wear, 245 53-60(2000) ate of the C/SiC composites was only 1/10-1/20 of that of the M. Hsu. "Wear and Wear Transition Mechanisms of cer- Ti alloy, and the deformation was only 1/10 of that caused by [-2]112-2(1996) ues-Carmes. " Wear Mechanism of silicon the Ti alloy Carbide: New Observations, " Wear, 174 [1-21239-42(1994)
IV. Conclusions (1) The hinge bearing with required good mechanical properties was made of 2D-C/SiC composites by CVI. The damaged specimen showed non-brittle failure behavior resulting from the pull-out of a single fiber and fiber cluster. The flexural strength and the compressive strength were 450 MP and 360 MPa, respectively. (2) The CVI process offered a potential method to manufacture the C/SiC composite hinge bearing of a stable and reliable friction property under a high load. With a material density of 2.03 g/cm3 , a constant friction coefficient was obtained as 0.68 on increasing the load up to 5800 N. (3) The hinge bearing based on C/SiC composites demonstrated good wear resistance and load-carrying ability due to the low wear and the small deformation under high loads. The wear rate of the C/SiC composites was only 1/10–1/20 of that of the Ti alloy, and the deformation was only 1/10 of that caused by the Ti alloy. (4) The grain abrasion is the main wear mechanism of a selfmated C/SiC composite hinge bearing with the testing framework. The wear was significantly determined by high load and cyclic mechanical stresses. A smooth and compact tribo-layer was formed, and the wear debris that remained in the wear track was ground to a very fine powder. The shallow grooves along the sliding direction were mainly caused by the relative movement of contact asperities. Load increased to a level above 3.5 kN led to several shallow cracks on the contact surface. References 1 H. G. Wulz and U. Trabandt, ‘‘Large Integral Hot CMC Structures Designed for Future Reusable Launchers’’; AIAA-97-2485, American Institute of Aeronautics and Astronautics, 1997. 2 R. Kladtke, N. Puttmann, and E. D. Graf, ‘‘X-38 European Partnership’’; AIAA 1999-99-4936, The American Institute of Aeronautics and Astronautics, 1999. 3 H. Hald and H. Weihs, ‘‘Development of Hot CMC Structures for Space Reentry Vehicles Via Flight Experiments’’; International Air and Space Symposium and Exposition, AIAA 2003-2696, 2003. 4 A. Muhlratzer and H. Pfeiffer, ‘‘CMC Body Flaps for The X-38 Experimental Space Vehicle,’’ Ceram. Eng. Sci. Pro., ABI/INFORM Trade & Industry, 23 [3] 331–8 (2002). 5 M. Ortelt, H. Weihs, I. Fischer, and M. Dogigli, ‘‘Thermal–Mechanical Quali- fication Tests of Complex CMC Re-Entry Structures,’’ Ceram. Eng. Sci. Pro., ABI/INFORM Trade & Industry, 24 [4] 281–7 (2003). 6 Robert L. Fusaro, ‘‘Preventing Spacecraft Failures Due to Tribological Problem’’; 2001 Annual Meeting, Society of Tribologists and Lubrication Engineers, NASA/TM—2001-210806, Orlando, FL, 20–24, 2001. 7 W. Krenkel, B. Heidenreich, and R. Renz, ‘‘C/C–SiC Composites for Advanced Friction Systems,’’ Adv. Eng. Mater., 4, 427–36 (2002). 8 Z. S. Pak, ‘‘Cf/SiC/C Composites for Tribological Application,’’ Key Eng. Mater., 164–165, 820–5 (1999). 9 S. Vaidyaraman, M. Purdy, T. Walker, and S. Horst, ‘‘C/SiC Material Evaluation for Aircraft Brake Application,’’ Key Eng. Mater., 164–165, 802–8 (1999). 10J.-Y. Paris, L. Vincent, and J. Denape, ‘‘High-Speed Tribological Behavior of a Carbon/Silicon Carbide Composite,’’ Com. Sci. Tech., 61 [3] 417–23 (2001). 11B. Venkataraman and G. Sundararajan, ‘‘The Influence of Sample Geometry on the Friction Behaviour of Carbon–Carbon Composites,’’ Acta Mater., 50, 1153–6 (2002). 12S.-J. Cho, C.-D. Um, and S.-S. Kim, ‘‘Wear and Wear Transition Mechanism in Silicon Carbide During Sliding,’’ J. Am. Ceram. Soc., 78 [4] 1076–8 (1995). 13T. E. Fischer, Z. Zhu, H. Kim, and D. S. Shin, ‘‘Genesis and Role of Wear Debris in Sliding Wear of Ceramics,’’ Wear, 245, 53–60 (2000). 14Y. Wang and S. M. Hsu, ‘‘Wear and Wear Transition Mechanisms of Ceramics,’’ Wear, 195 [1–2] 112–2 (1996). 15J. Takadoum, Z. Zsiga, and C. Roques-Carmes, ‘‘Wear Mechanism of Silicon Carbide: New Observations,’’ Wear, 174 [1–2] 239–42 (1994). & Fig. 11. Contact surfaces of carbon fiber reinforced silicon carbide matrix (C/SiC) after friction against a C/SiC ring under a load of 3.5 kN and a constant sliding velocity of 33 103 m/s. April 2007 High-Load Friction of a C/SiC Hinge Bearing 1145
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